Propane warning sign for windows



FIG. 1 is a front elevational view of a propane warning sign for windows showing my new design, with the rear being flat and unornamented and with the broken line showing for illustrative purposes only and forming no part of the claimed design; and,

FIG. 2 is a top plan view thereof, with the bottom being a mirror image. 

The ornamental design for a propane warning sign for windows, as shown and described. 